Pharmacologically relevant—known blockers show dose-dependent inhibition in a large signal window

The FluxOR™ Potassium Ion Channel Assays are the next generation solution for high throughput screening (HTS) of potassium ion channel and transporter activities. The FluxOR assays take advantage of the well described permeability of potassium channels to thallium (Tl+) ions and the utilization of a new and improved indicator dye that results in a larger signal window and a significant improvement in the sensitivity of the assay. With more than 80 distinct potassium ion channel isoforms, the fluorescent signal reported in this assay serves as a surrogate readout of the activity of any ion channel or transporter that is permeant to thallium, including hERG, Kv1.3, Kir2.1, KATP, and many other of >80 distinct potassium ion channel gene products. The FluxOR assays has been validated in cells expressing potassium channels either stably or transiently, in 96-, 384- and 1,536 well plate formats.

Assay Principle

To run the assay, cells are loaded with non-fluorescent, thallium-specific FluxOR™ dye (Figure 1). Drugs to be screened are pre-incubated with the cells and the microplates are loaded into the reader, where they are injected with a stimulus buffer containing a low level of thallium ions. The thallium ions freely flow through open potassium channels, acting as a surrogate for K+. When the potassium channel is stimulated, thallium flows into the cell and binds the FluxOR™ dye, generating a fluorescent signal, proportional to channel activity—in physiological saline conditions. Multiple potassium ion channels including Kv1.3 (Figure 2), Kv7.2/Kv7.3 (Figure 3), Kv11.1 (hERG) (Figure 4), Kir1.1, Kir2.1, Kv1.1, Kv2.1 (data not shown) have been demonstrated to work with the FluxOR assay for reliable results.

Figure 1. Principle of the FluxOR™ assay. Basal fluorescence from cells loaded with the FluxOR™ dye is low, as shown in the left panel, until potassium channels are stimulated. When thallium is added to the assay with the stimulus, the thallium flows down its concentration gradient into the cells, activating the dye as shown in the right panel.

FluxOR Potassium Ion Channel Assay

FluxOR II Green Potassium Ion Channel Assay

FluxOR Red Potassium Ion Channel Assay

Assay principle

Uses thallium (Tl+ ) ions as surrogate for potassium ions. Thallium is added to the extracellular solution, potassium channels are open, thallium flows down its concentration gradient into the cells, and channel or transporter activity is detected with a proprietary indicator dye that increases in cytosolic fluorescence